首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   947篇
  免费   23篇
  国内免费   35篇
教育   301篇
科学研究   85篇
各国文化   3篇
体育   425篇
综合类   188篇
信息传播   3篇
  2023年   1篇
  2022年   5篇
  2021年   15篇
  2020年   20篇
  2019年   16篇
  2018年   11篇
  2017年   18篇
  2016年   18篇
  2015年   32篇
  2014年   45篇
  2013年   65篇
  2012年   53篇
  2011年   86篇
  2010年   47篇
  2009年   51篇
  2008年   59篇
  2007年   54篇
  2006年   58篇
  2005年   60篇
  2004年   51篇
  2003年   49篇
  2002年   27篇
  2001年   32篇
  2000年   32篇
  1999年   25篇
  1998年   15篇
  1997年   16篇
  1996年   14篇
  1995年   8篇
  1994年   9篇
  1993年   8篇
  1992年   5篇
排序方式: 共有1005条查询结果,搜索用时 15 毫秒
1.
BackgroundLycium barbarum (also called wolfberry), a famous Chinese traditional medicine and food ingredient, is well recognized for its significant role in preventing obesity; however, the molecular mechanisms underlying its preventive effects on fat accumulation are not well understood yet. The aim of this study was to determine the effects and mechanism of Lycium barbarum polysaccharides (LBP) on the proliferation and differentiation of 3T3-L1 preadipocytes. MTT was used to detect the proliferation of 3T3-Ll preadipocytes. Oil red O staining and colorimetric analysis were used to detect cytosolic lipid accumulation during 3T3-L1 preadipocyte differentiation. Real-time fluorescent quantitative PCR (qPCR) technology was used to detect peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein α (C/EBPα), adipocyte fatty-acid-binding protein (aP2), fatty acid synthase (FAS), and lipoprotein lipase (LPL) expression.ResultsThe concentration of LBP from 25 to 200 μg/mL showed a tendency to inhibit the growth of preadipocytes at 24 h, and it inhibited the differentiation of 3T3-L1 preadipocytes in a dose-dependent manner. In the preadipocytes treated with 200 μg/mL LBP, there were reduced lipid droplets in the cytoplasm, and its effect was opposite to that of rosiglitazone (ROS), which significantly reduced the PPARγ, C/EBPα, aP2, FAS, and LPL mRNA expression of adipocytes.ConclusionsLBP exerts inhibitive effects on the proliferation and differentiation of 3T3-L1 preadipocytes and decreases the cytoplasm accumulation of lipid droplets during induced differentiation of preadipocytes toward mature cells. Above phenomenon might link to lowered expression of PPARγ, C/EBPα, aP2, FAS, and LPL after LBP treatment. Thus, LBP could serve as a potential plant extract to treat human obesity or improve farm animal carcass quality via adjusting lipid metabolism.How to cite: Xu X, Chen W, Yu S, et al. Inhibition of preadipocyte differentiation by Lycium barbarum polysaccharide treatment in 3T3-L1 cultures. Electron J Biotechnol 2021;50. https://doi.org/10.1016/j.ejbt.2021.01.003  相似文献   
2.
The aim of this study was to evaluate the safety of an antiviral regimen of protease inhibitors combined with Arbidol (umifenovir) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pneumonia patients. The genomic sequence of SARS-CoV-2 is highly homologous to that of SARS-CoV (Zhou et al., 2020). Previously published basic and clinical research on anti-SARS-CoV treatment found that lopinavir/ritonavir (LPV/r) could improve the prognosis of SARS patients (Chan et al., 2003; Chu et al., 2004). Darunavir (DRV) is another protease inhibitor that blocks the binding of SARS-CoV-2 to human angiotensin-converting enzyme 2 (Omotuyi et al., 2020). The broad-spectrum antiviral drug Arbidol (umifenovir) also shows in vitro anti-SARS-CoV activity (Khamitov et al., 2008).  相似文献   
3.
Abstract

Carnosine was originally discovered in skeletal muscle, where it exists in larger amounts than in other tissues. The majority of research into the physiological roles of carnosine have been conducted on skeletal muscle. Given this and the potential for muscle carnosine content to be increased with supplementation, there is now a large body of research examining the ergogenic effects (or otherwise) of carnosine. More recent research, however, points towards a potential for carnosine to exert a wider range of physiological effects in other tissues, including the brain, heart, pancreas, kidney and cancer cells. Taken together, this is suggestive of a potential for carnosine to have therapeutic benefits in health and disease, although this is by no means without complication. Herein, we will provide a review of the current literature relating to the potential therapeutic effects of carnosine in health and disease.  相似文献   
4.
In this study we examined what are the markers of immigrant naturalisation as seen from the perspectives of recipient nationals. Social markers are perceptual signposts that receiving nationals use in deciding whether a non-native born is a member of the destination country. In short, what should immigrants do in order to be accepted by receiving nationals as “one of us”. Cross national data on 20 indicators of “everyday nationhood” were collected from five countries – Singapore, Japan, Australia, Finland, and Canada. The markers highlight common dispositions, activities, or social norms that are associated with citizenship. Exploratory factor analysis in each sample consistently demonstrated a two-factor structure model that supports the contemporary ethnic-civic distinction, but the markers that make up each of the two dimensions vary between countries. No metric equivalence was found, and that the markers have culture-specific meanings. The framework offers a novel insight to intercultural relations. The results suggest that adaptation and social inclusion need to consider the norms and values practised in the recipient society, and how immigration may redefine intergroup boundaries.  相似文献   
5.
Living birds are unique among vertebrates in the formation of a female-specific bone tissue called medullary bone (MB) that is strictly associated with reproductive activity. MB is a rapidly mobilized source of calcium and phosphorus for the production of eggshell. Among living taxa, its skeletal distribution can be highly extensive such that it even exists in the ribs of some species. Due to its ephemeral nature, MB is rarely fossilized and so little is understood with regard to the origin of MB and its skeletal distribution in early taxa. Here we describe a new Early Cretaceous enantiornithine bird, Mirusavis parvus, gen. et. sp. nov., indicating that skeleton-wide distribution of MB appeared early in avian evolution. We suggest that this represents the plesiomorphic condition for the Aves and that the distribution of MB observed among extant neornithines is a product of increased pneumatization in this lineage and natural selection for more efficient distribution of MB.  相似文献   
6.
宋璐璐  曹植  代敏 《资源科学》2021,43(3):501-512
中国是全球最大的汽车制造和消费国,汽车行业带来的资源消耗和温室气体排放受到了学者的广泛关注。辨析汽车行业的物质资源代谢特征和碳减排潜力可为落实循环经济政策和实现可持续发展提供科学依据。本文基于动态物质流模型,预测了中国乘用车中21种物质材料的代谢特征,评估了乘用车使用过程中的碳减排潜力。研究结果表明:①1949—2019年中国乘用车中的物质存量呈现指数型增长趋势,由2.3万t增加至3.7亿t。2030年后物质存量逐渐饱和,并于2050年达到5.6亿~11.1亿t;②2050年乘用车中物质材料报废量将超过需求量并达到37.4百万~73.8百万t/年;其中,钢铁(包括高强钢、普通钢和铁)报废量将达到21.2百万~42.4百万t/年;其他战略金属和稀贵金属报废量将达到36.8万~59.8万t/年;延长乘用车使用寿命以及较低的乘用车保有量可有效减少产废量;③提高汽油车的燃料效率是最有效的碳减排策略,其碳减排潜力高达3.3亿t,可降低40%的碳排放量。本文的研究结果可为汽车行业物质资源的有效管理以及碳减排策略的制定提供科学支撑。  相似文献   
7.
8.
目的:评价规律运动对成年人糖脂代谢的影响效果,为预防和控制糖脂代谢紊乱提供科学的锻炼指导。方法:检索中国知网、万方、维普数据库,收集关于规律运动对成年人糖脂代谢影响的研究成果,采用Cochrane偏倚风险评估工具对文献质量进行评估,采用RevMan 5.2进行Meta分析。结果:共纳入17篇研究文献,其中较高质量的2篇、中等质量的8篇、低等质量的7篇;Meta分析结果显示,与对照组相比较,规律运动能够有效降低机体的血糖、甘油三酯和总胆固醇含量,增加高密度脂蛋白含量,但规律运动对于降低低密度脂蛋白含量没有显著效果;进一步亚组分析结果显示,规律运动的干预时间无论长短均与血糖含量存在显著差异,但多于3个月时才能降低甘油三酯、总胆固醇含量,增加高密度脂蛋白含量。结论:规律运动能够有效改善糖脂代谢水平,当运动持续时间多于3个月,改善糖脂代谢水平的效果将更明显。  相似文献   
9.
ABSTRACT

The systematic review and meta-analysis evaluated the effect of aerobic, resistance and combined exercise on RMR (kCal·day-1) and performed a methodological assessment of indirect calorimetry protocols within the included studies. Subgroup analyses included energy/diet restriction and body composition changes. Randomized control trials (RCTs), quasi – RCTs and cohort trials featuring a physical activity intervention of any form and duration excluding single exercise bouts were included. Participant exclusions included medical conditions impacting upon RMR, the elderly (≥65 years of age) or pregnant, lactating or post-menopausal women. The review was registered in the International Prospective Register of Systematic Reviews (CRD 42,017,058,503). 1669 articles were identified; 22 were included in the qualitative analysis and 18 were meta-analysed. Exercise interventions (aerobic and resistance exercise combined) did not increase resting metabolic rate (mean difference (MD): 74.6 kCal·day-1[95% CI: ?13.01, 161.33], P = 0.10). While there was no effect of aerobic exercise on RMR (MD: 81.65 kCal·day-1[95% CI: ?57.81, 221.10], P = 0.25), resistance exercise increased RMR compared to controls (MD: 96.17 kCal·day-1[95% CI: 45.17, 147.16], P = 0.0002). This systematic review effectively synthesises the effect of exercise interventions on RMR in comparison to controls; despite heterogenous methodologies and high risk of bias within included studies.  相似文献   
10.
文章从句法环境和语用功能两个方面分析了“你V”类话语标记的使用倾向,认为这些差异在一定程度上是受到语义俯瞰的制约和影响.话语标记的使用倾向反映出其语法化程度的高低.总体而言,“你V”的语法化程度从高到低依次为:“你看”>“你说”>“你想”>“你知道”,这一结果是由“V”的表义功能、“V”的词性类别、“你V”的适用语体以及“你V”的音节数目等因素的共同作用造成的.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号